(1) Field of the Invention
The present invention relates to an image compositing apparatus using texture mapping, in an appliance in which computer graphics are applied.
(2) Description of the Prior Art
Conventionally, in the field of computer graphics, there has been a technique which creates an image enhanced in reality, 3-D feeling and surface texture, when compared to the image created by only polygons, by mapping a variety of patterns, pictures and photographs etc. onto the surfaces of polygon objects.
For example, when a photograph of a brick wall has been mapped onto the surface of a single planar polygon object, it is possible to create a brick wall having a real representation enhanced in surface texture without using a number of brick-like polygon objects.
Use of this technique enables creation of a variety of virtual 3-D spaces and can be applied to simulations, virtual reality, computer games, such as representations of a walk-through in a building, flight simulators, racing games, etc.
In particular, in the field where images need to be formed in real time, such as virtual reality, arcade games, the texture mapping technique which needs fewer calculations for processing of polygons is used very often to enhance the reality of a virtual space.
Japanese Patent Application Laid-Open Hei 6 No. 348,860 has proposed an image compositing apparatus wherein, each image of the polygons of a 3-D object obliquely observed from a typical plurality of angles of view located along the path of movement of the view-point coordinate system, is stored beforehand as texture information, and each of the polygons of the above three-dimensional object is mapped with the texture information which corresponds to the positional relation between the view-point coordinate system and the three-dimensional object, to thereby represent an oblique image of a 3-D object using a lower number of polygons.
Further, Japanese Patent Application Laid-Open Hei 8 No. 161,510 has proposed a texture mapping apparatus, wherein mapping is performed by extracting optical polygon dividing points in accordance with the size of a polygon to be mapped, to thereby produce a natural, realistic, mapping image with fewer calculations.
In using a texture mapping technique, for example, when a space having a certain depth, e.g., two continuous rooms is rendered, the image of the next room to the rear is represented as a texture, and this may be mapped onto the single polygon which is located at the partitioning plane between the two rooms, it is possible to render a space having depth using a lower number of polygons, without needing object representation of the rear room.
However, since in this case, the image of the next room is represented as a texture, viewed from a particular point, the perspective of the images of the front room and rear room will not align with each other when the view-point is moved from that at which the texture image was prepared.
In the image compositing apparatus disclosed in Japanese Patent Application Laid-Open Hei 6 No. 348,860, the movement of the view point of the observer should be predicted beforehand and a number of patterns of images viewed from required angles of view should be prepared in advance, needing a large size of texture memory.
Moreover, the texture mapping apparatus disclosed in Japanese Patent Application Laid-Open Hei 8 No. 161,510 is a type which eliminates distortion and perspective of the texture map within a single polygon to be mapped so as to produce a natural texture image, but not a type which considers the discordance of perspective between the polygon and its surrounding, occurring as the observer moves.